Methods of lithographically patterning a substrate

ABSTRACT

A method of lithographically patterning a substrate that has photoresist having removal areas and non-removal areas includes first exposing at least the non-removal areas to radiation effective to increase outer surface roughness of the photoresist in the non-removal areas at least post-develop but ineffective to change photoresist solubility in a developer for the photoresist to be cleared from the non-removal areas upon develop with the developer. Second exposing of radiation to the removal areas is conducted to be effective to change photoresist solubility in the developer for the photoresist to be cleared from the removal areas upon develop with the developer. The photoresist is developed with the developer effective to clear photoresist from the removal areas and to leave photoresist in the non-removal areas that has outer surface roughness in the non-removal areas which is greater than that before the first exposing. Other implementations and embodiments are contemplated.

RELATED APPLICATION DATA

This patent resulted from a divisional application of U.S. patentapplication Ser. No. 11/868,328 filed Oct. 5, 2007, which isincorporated by reference herein.

TECHNICAL FIELD

Embodiments disclosed herein pertain to methods of lithographicallypatterning substrates.

BACKGROUND

A continuing goal in semiconductor processing is increasedminiaturization while maintaining high performance. Modern semiconductorprocesses are still heavily reliant on lithography in fabricatingintegrated circuitry to achieve this goal.

Photolithography is a commonly-used method for patterning featuresduring semiconductor processing. A radiation-sensitive material (i.e.,photoresist) is formed over a substrate which is ultimately to bepatterned, for example by etching or ion implanting. The photoresist issubsequently subjected to radiation which modifies the solubility of theimpacted versus the non-impacted regions in a suitable developersolvent. Accordingly, the radiation is provided in a desired pattern sothat some portions of the photoresist are impacted by the radiationwhile other portions of the photoresist are not impacted by theradiation. The photoresist is then subjected to developing conditionswhich selectively remove either the impacted or the non-impactedportions. Photoresists are designated to be either negative or positive.If the photoresist is a positive photoresist, the impacted portions areselectively removed. If the photoresist is a negative photoresist, thenon-impacted portions are selectively removed.

The photoresist remaining after development defines a patterned mask onthe substrate. The pattern of such mask can be subsequently transferredto the underlying material using appropriate etching and/or implantingtechniques to form patterned features in material beneath the mask.

A problem which motivated embodiments of the invention disclosed hereinpertains to water marks that remain over a positive photoresist layerafter develop patterning. During develop or thereafter, the photoresistmay be exposed to water, which can leave water marks on the outersurface of the photoresist. Such are commonly crystalline or otherresidual material which essentially deposits as a thin layer over thetop of the photoresist in a blotchy and unpredictable manner. Some ofthese water marks actually extend over and into openings within thedeveloped photoresist. Such can, of course, adversely affect subsequentprocessing of the substrate using the photoresist as a mask. Regardless,the patterned photoresist typically undergoes a post-developmentinspection or analysis prior to subsequent substrate processing usingthe mask to determine quality of the patterning of the photoresist mask.The water marks remaining over the substrate can adversely impact thisinspection and analysis.

While embodiments of the invention were motivated in addressing theabove-identified issues, it is no way so limited. Embodiments disclosedherein are only limited by the accompanying claims as literally worded,without interpretive or other limiting reference to the specification,and in accordance with the doctrine of equivalence.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic sectional view of substrate in process inaccordance with an aspect of the invention.

FIG. 2 is a view of the FIG. 1 substrate at a processing step subsequentto that shown by FIG. 1.

FIG. 3 is a view of the FIG. 1 substrate at a processing step subsequentto that shown by FIG. 1, and alternate or in addition to that shown byFIG. 2.

FIG. 4 is a view of the FIG. 2 substrate at a processing step subsequentto that shown by FIG. 2.

FIG. 5 is a view of the FIG. 4 substrate at a processing step subsequentto that shown by FIG. 4.

FIG. 6 is a plot of post-develop thickness of a photoresist as afunction of incident radiation in millijoules of a reduction-to-practiceexample embodiment of the invention.

FIG. 7 is a diagrammatic sectional view of substrate in process inaccordance with an aspect of the invention.

FIG. 8 is a view of the FIG. 7 substrate at a processing step subsequentto that shown by FIG. 7.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Example embodiments of methods of lithographically patterning asubstrate are initially described with reference to FIGS. 1-5. Referringto FIG. 1, a substrate is indicated generally with reference 10. In oneembodiment, substrate 10 may comprise a semiconductor substrate. In thecontext of this document, the term “semiconductor substrate” or“semiconductive substrate” is defined to mean any constructioncomprising semiconductive material, including, but not limited to, bulksemiconductive materials such as a semiconductive wafer (either alone orin assemblies comprising other materials thereon), and semiconductivematerial layers (either alone or in assemblies comprising othermaterials). The term “substrate” refers to any supporting structure,including, but not limited to, the semiconductive substrates describedabove.

Substrate 10 is depicted as comprising material or region 12 having aphotoresist 14, for example a positive photoresist, formed thereover.Region 12 may be homogenous or non-homogenous, and may include numerousmaterials, devices, regions, and/or components fabricated therein.Regardless, photoresist 14 may be considered as comprising removal areas16 and non-removal areas 18. Removal areas 16 are to be radiatedeffective to change photoresist solubility in a developer to be able toclear photoresist from such removal areas upon develop with thedeveloper, and with non-removal areas 18 not to be so radiated, and aswill be apparent from the continuing discussion.

Photoresist 14 can be considered as having an outer surface 20 whichwill be exposed to radiation. In some embodiments herein, such exposingmay be referred to as a “first exposing” or as a “second exposing” forconvenience and differentiation with respect to each as will be apparentfrom the continuing discussion. However, reference to “first” and“second” do not require temporal order between the two. In other words,the first exposing may occur prior to the second exposing, or the secondexposing may occur prior to the first exposing. Further in someembodiments, the first exposing and the second exposing may occurconcurrently. Also, additional exposure to radiation may occur before,after, or between the stated first exposing and second exposing.

Referring to FIG. 2, a first exposing to radiation has been conducted atleast to non-removal areas 18 of photoresist 14. Such first exposing isindicated generally, by way of example only, by downwardly directedarrows 22. In one embodiment, the first exposing is effective toincrease at least the post-develop outer surface roughness of thephotoresist in the non-removal areas, but is ineffective to changephotoresist solubility in a developer for the photoresist to be clearedfrom non-removal areas 18 upon develop with the developer. However, somephotoresist may be removed in the non-removal areas during develop withthe developer, and the first exposing may have some impact thereon.Regardless, the first exposing may or may not also be effective toincrease pre-develop outer surface roughness of the photoresist as wellas post-develop roughness.

The first exposing may or may not be through a mask. Regardless,exposure to radiation during the first exposing may or may not also beof removal areas 16, with exposure of removal areas being shown in FIG.2. If removal areas 16 are exposed to the radiation during the firstexposing, such is of course immaterial to post-develop roughness thereofas photoresist in removal areas 16 will ultimately be cleared from thesubstrate upon develop. Where the first exposing is also of removalareas 16, such might be blanket over the whole substrate (for example atthe same time), or might not be blanket over the whole substrate, forexample being in a stepped separate manner over different areas of thesubstrate. Regardless, where a mask is used, and regardless of whetherthe first exposing is also of the removal areas, the first exposingmight or might not be through transparent openings in a mask.

FIG. 3 depicts an alternate embodiment first exposing to that of FIG. 2.In FIG. 3, a mask 25 is used. Such is depicted as comprising radiationblocking regions 26 and radiation transmissive regions 28 with respectto the selected wavelength and quanta/dose of incident radiation 22which is used. Blocking regions 26 are shown to correspond (by way ofexample only) in size and dimension to removal areas 16, and maskopenings 28 are shown to correspond in size and dimension to non-removalareas 18. Mask openings 28 are depicted as extending completely throughmask 25, although such openings might comprise one or more materials thecombination of which is effectively transmissive of incident radiation22 for the first exposing.

Referring to FIG. 4, second exposing has been conducted of removal areas16 to radiation (indicated by arrows 35) effective to change photoresistsolubility in the developer for the photoresist to be cleared fromremoval areas 16 upon develop with the developer, as will be describedbelow. By way of example only, FIG. 4 depicts the second exposing ashaving been conducted using a mask 30 having radiation opaque regions 24effective to preclude transmission of incident radiation 35 tonon-removal areas 18 so that such are not so effectively radiated duringthe second exposing.

The above-described FIGS. 1-4 embodiments depict an example wherein thefirst exposing occurs prior to the second exposing. However, the secondexposing might occur prior to the first exposing. For example, theexposing of FIG. 4 could be conducted prior to either of the exampleFIG. 2 or 3 exposings. In one embodiment, the first exposing and thesecond exposing are with radiation of the same wavelength with respectto each. However, the first and second exposing may be with radiation ofdifferent wavelengths. Also, the first and second exposings might beconducted at the same time. Regardless and by way of example only, thefirst exposing might be conducted in a single exposure step or overmultiple exposure steps. Further, the second exposing might be conductedin a single exposure step or over multiple exposure steps.

Referring to FIG. 5, and after the first exposing and after the secondexposing, photoresist 14 is depicted as having been developed with thedeveloper (for example by applying or otherwise exposing the developerto removal areas 16 and to non-removal areas 18) effective to clearphotoresist 14 from removal areas 16, and to leave photoresist 14 innon-removal areas 18 that has outer surface 20 a roughness innon-removal areas 18 which is greater than what it was before the firstexposing. Of course, some thickness of the photoresist might also beremoved from the non-removal areas and if so at least some photoresistwill remain thereover. In one embodiment, the first exposing iseffective to increase post-develop photoresist outer surface RMS (rootmean squared) roughness in the non-removal areas which can be at least25% greater than that before the first exposing, in one embodiment atleast 50% greater, and in another embodiment at least 100% greater.

In one embodiment, at least non-removal areas 18 of photoresist 14 areexposed to liquid water at least one of during or after the developing,and the increase in roughness reduces the amount of photoresist outersurface water marks (i.e., either in one or both of number or size) innon-removal areas 18 than would otherwise occur under identicalprocessing but for the first exposing. Such reduction in amount of watermarks might be only partial, or might be essentially complete such thatno water marks exist post-develop after any exposure of photoresist 14to water either during or after developing. Without being limited by anytheory of operation or theory of invention, it is believed that outersurface roughening as just-described is what facilitates reduction inpost-develop water marks, although such might result from otherphenomena whether alone or in combination with roughening. However andregardless, not all embodiments of the invention require roughening, nordo all embodiments of the invention require post-develop reduction inwater marks, with the invention being limited by the accompanying claimsas literally worded and in accordance with the doctrine of equivalence.

The invention was reduced-to-practice using SAIL X0181 photoresistavailable from ShinEtsu MicroSi of Phoenix, Ariz. Such was deposited toa deposition thickness of about 1,300 Angstroms, and incident radiationduring the first and second exposings was deep ultraviolet radiationhaving a wavelength of 193 nanometers. Accordingly, in areduction-to-practice example, the same radiation wavelength was usedduring both the first and second stated exposings. Alternatephotoresists and alternate radiation including different wavelengths areof course also contemplated.

FIG. 6 depicts a graph of post-develop thickness in Angstroms as afunction of incident radiation dose in millijoules (mJ) for the abovereduction-to-practice photoresist using 193 nanometer incidentradiation. Such is depicted as having a dose-to-clear point E₀ of about5.4 millijoules and a develop drop-off point E_(D) of about 5millijoules. In the context of this document, a “develop drop-off point”is that first dose of selected incident radiation for a photoresistwherein post-develop thickness experiences an initial thicknessreduction of at least 150 Angstroms for the next 0.1 millijoule increasein radiation dose. In reduction-to-practice examples using the aboveexample photoresist, incident dose of 3.0 millijoules did not result ineither roughness increase nor post-develop reduction in the amount ofphotoresist outer surface water marks. However, incident radiation doseof 4.0 millijoules did result in both an increase in photoresist outersurface roughness in RMS and a decrease in photoresist outer surfacewater mark amount.

In a reduction-to-practice example, a first incident radiation dose of 4millijoules resulted in a photoresist outer surface RMS roughnesspost-develop which was greater than that of the same photoresist priorto exposure to the 4 millijoule incident radiation dose. Of course,different photoresists and different incident wavelength radiation mightresult or experience different RMS values and/or different degree inamount of reduction of water marks in the photoresist outer surfacepost-develop. Further, use of different photoresists and/or differentwavelength of incident radiation will likely produce different pointsE_(D) and E₀, as well a different shape of the FIG. 6 plot. Regardless,in one embodiment in a method of lithographically patterning asubstrate, the second exposing to the removal areas is at a value of E₀or greater to effectively enable clearing of photoresist therefrom informing a desired mask pattern on a substrate.

In one embodiment, a method of lithographically patterning a substratecomprises forming photoresist over a substrate, wherein the photoresisthas a develop drop-off point (for example in millijoules) for a selectedincident radiation wavelength. The photoresist comprises removal areasand non-removal areas, for example as described above in connection withFIG. 1.

First exposing is conducted of at least the non-removal areas to a doseof the selected radiation wavelength below and within 30% (for example,in units of millijoules) of the develop drop-off point. The dose duringthe first exposing is ineffective to change photoresist solubility inthe developer for the photoresist to be cleared in the non-removal areasupon develop with the developer. By way of example only, FIGS. 2 and 3depict such example processing. In one embodiment, the first exposingcan be below and within 25% of the develop drop-off point, and in otherexample embodiments below and within 20%, below and within 15%, belowand within 10%, and below and within 5% of the develop drop-off point.

Second exposing is conducted of the removal areas to a dose of theselected radiation wavelength which is at or above the develop drop-offpoint. The second exposing dose is effective to change photoresistsolubility in the developer for the photoresist to be cleared in theremoval areas upon develop with the developer. By way of example only,FIG. 4 depicts, and the above text pertaining thereto describes, suchexample processing. The first exposing might occur before or after thesecond exposing, or the first exposing and the second exposing mightoccur concurrently.

After the first exposing and the second exposing, the photoresist isdeveloped with the developer effective to clear photoresist from theremoval areas and to leave photoresist in the non-removal areas. Ofcourse, some thickness of the photoresist might also be removed from thenon-removal areas and if so at least some photoresist will remainthereover.

The first exposing may or may not be effective to increase photoresistouter surface roughness in the non-removal areas at least post-develop.Further and regardless, the first exposing may or may not be effectiveto reduce amount of photoresist outer surface water marks in thenon-removal areas than would otherwise occur under identical processingbut for the first exposing where at least the non-removal areas areexposed to liquid water at least one of during or after the developing.

Another embodiment, by way of example only, is shown and described inconjunction with FIGS. 7 and 8 with respect to an example first exposingand an example second exposing occurring concurrently. Referringinitially to FIG. 7, a substrate 10 with photoresist 14 is depicted. Amask 50 has been provided over photoresist 14. Mask 50 has firstradiation transmissive regions 52 which may define removal areas 16, andhas second radiation transmissive regions 54 which may definenon-removal areas 18. Transmissive regions 52 and 54 may of coursedefine removal areas or non-removal areas independent of each other, anduse of such transmissive regions for specific applications will beunderstood by one skilled in the art. One transmissive region may bemore or less transmissive to a selected wavelength than anothertransmissive region. For example, second radiation transmissive regions54 can be less transmissive of radiation of a selected wavelength thanfirst radiation transmissive regions 52. For example, differentmaterials and/or thicknesses of material might be utilized in differentregions 52 and 54 to effectuate such transmissive differences.

Referring to FIG. 8, radiation of the selected wavelength contacts orimpinges onto mask 50, as indicated generally by downwardly directedarrows 55. In one embodiment, mask 50 passes or allows impingingradiation 55 through second radiation transmissive regions 54 effectiveto increase photoresist outer surface roughness in non-removal areas 18at least post-develop. However, the radiation allowed through isineffective to change photoresist solubility in a developer for thephotoresist to be cleared from non-removal areas 18 upon develop withthe developer. In one example, the material in second radiationtransmissive regions 54 is completely covering thereof (as shown) and ofa thickness and material sufficient to allow passage of radiationthere-through to impart such increase in surface roughness innon-removal areas 18. In another example, the material in secondradiation transmissive regions 54 is largely radiation opaque and notcompletely covering thereof forming a spaced pattern of sub-resolutionfeatures (not shown) in regions 54 that is still sufficient to allowpassage of radiation there-through, for example to impart such increasein surface roughness in non-removal areas 18. Mask 50 allows impingingradiation through first radiation transmissive regions 52 effective tochange photoresist solubility in the developer for the photoresist to becleared from removal areas 16 upon develop with the developer.

After the impinging, the photoresist is developed with the developer(for example by applying or otherwise exposing the developer to theremoval areas and to non-removal areas 18) effective to clearphotoresist from the removal areas and to leave photoresist in thenon-removal areas that has outer surface roughness which is greater thanthat before the impinging, for example as described above and shown inconnection with FIG. 5. Such passing or allowing of impinging radiationthrough second radiation transmissive regions 54 may or may not reduceamount of photoresist outer surface water marks in the non-removal areasthen would otherwise occur under identical processing but for saidpassing of impinging radiation through second radiation transmissiveregions 54. Any of the attributes and processing otherwise as describedabove may additionally be utilized and/or occur.

In one embodiment, impinging of radiation of the selected wavelengthonto a mask 50 as shown in FIG. 8 passes or allows the impingingradiation through second radiation transmissive regions 54 below andwithin 30% of the develop drop-off point. Yet, such passing of radiationis ineffective to change photoresist solubility for the photoresist tobe cleared from the non-removal areas upon develop with the developer.Such passing of impinging radiation through second radiationtransmissive regions 54 may or may not be effective to increasephotoresist outer surface roughness in the non-removal areas at leastpost-develop. Further and regardless, such passing of impingingradiation through second radiation transmissive regions 54 may or maynot be effective in reducing amount of photoresist outer surface watermarks in the non-removal areas where such are exposed to liquid water atleast one of during or after the developing. Any of the processing andattributes as described above are also of course contemplated.

In one embodiment where water mark reduction occurs, such may beindependent of roughening effect or other parameters regarding a firstexposing and a second exposing. For example, first exposing of radiationmay be conducted at least to the non-removal areas to be ineffective tochange photoresist solubility in a developer for the photoresist to becleared from the non-removal areas upon develop with the developer. Asecond exposing of radiation may be conducted to the removal areas to beeffective to change photoresist solubility in the developer for thephotoresist to be cleared from the removal areas upon develop with thedeveloper. After the first exposing and the second exposing, thephotoresist is developed with the developer effective to clearphotoresist from the removal areas and to leave photoresist in thenon-removal areas. At least the non-removal areas of the photoresist areexposed to liquid water at least one of during or after the developing.The first exposing reduces the amount of outer surface water marks inthe non-removal areas of the photoresist post-develop than wouldotherwise occur under identical processing but for the first exposing.Any or the processing and attributes as described above are also ofcourse contemplated.

In compliance with the statute, the subject matter disclosed herein hasbeen described in language more or less specific as to structural andmethodical features. It is to be understood, however, that the claimsare not limited to the specific features shown and described, since themeans herein disclosed comprise example embodiments. The claims are thusto be afforded full scope as literally worded, and to be appropriatelyinterpreted in accordance with the doctrine of equivalents.

The invention claimed is:
 1. A method of lithographically patterning asubstrate comprising photoresist which has removal areas and non-removalareas, the photoresist having a develop drop-off point for a selectedincident radiation wavelength, the method comprising: first exposing atleast the non-removal areas to a dose of the selected radiationwavelength which is below and within 30% of the develop drop-off pointto be ineffective to change a photoresist solubility in a developer forthe photoresist to be cleared from the non-removal areas upon developingwith the developer, an incident dose of radiation of the selectedradiation wavelength being at least 4.0 millijoules, the first exposingincreasing a photoresist post-develop root mean squared surfaceroughness by at least 25%; second exposing the removal areas to a seconddose of the selected radiation wavelength which is at or above thedevelop drop-off point effective to change the photoresist solubility inthe developer for the photoresist to be cleared from the removal areasupon developing with the developer; after the first exposing and thesecond exposing, developing the photoresist with the developer effectiveto clear photoresist from the removal areas and to leave photoresist inthe non-removal areas; and directly after the developing, exposing atleast the non-removal areas to liquid water.
 2. The method of claim 1wherein the first exposing dose is below and within 25% of the developdrop-off point.
 3. The method of claim 1 wherein the first exposing doseis below and within 20% of the develop drop-off point.
 4. The method ofclaim 1 wherein the first exposing dose is below and within 15% of thedevelop drop-off point.
 5. The method of claim 1 wherein the firstexposing dose is below and within 10% of the develop drop-off point. 6.The method of claim 1 wherein the first exposing dose is below andwithin 5% of the develop drop-off point.
 7. The method of claim 1wherein the first exposing dose is effective to increase outer surfaceroughness of the photoresist in the non removal areas at least after thedeveloping.
 8. The method of claim 1 comprising exposing at least thenon-removal areas of the photoresist to the liquid water at least one ofduring or after the developing, the first exposing reducing amount ofouter surface water marks in the non-removal areas of the photoresistthan would otherwise occur under identical processing but for the firstexposing.
 9. The method of claim 1 wherein the first exposing and thesecond exposing occur concurrently.
 10. The method of claim 1 whereinthe first exposing is blanket over the whole substrate.
 11. A method oflithographically patterning a substrate comprising a photoresist whichhas removal areas and non-removal areas, the method comprising:providing a mask over the photoresist, the mask having first radiationtransmissive regions and second radiation transmissive regions, thesecond radiation transmissive regions being less transmissive ofradiation than the first radiation transmissive regions; impingingradiation onto the mask, the mask allowing the impinging radiationthrough the second radiation transmissive regions effective to increasean outer surface roughness of the photoresist by at least 25% in thenon-removal areas at least post-develop but ineffective to change asolubility of the photoresist in a developer for the photoresist to becleared from the non removal areas upon developing with the developer,an incident dose of radiation being at least 4.0 millijoules, the maskallowing the impinging radiation through the first radiationtransmissive regions effective to change the solubility of thephotoresist in the developer for the photoresist to be cleared from theremoval areas upon develop with the developer; after the impinging,developing the photoresist with the developer effective to clear thephotoresist from the removal areas and to leave the photoresist in thenon-removal areas that has a second outer surface roughness in thenon-removal areas which is greater than that before the impinging; anddirectly after the developing, exposing at least the non-removal areasto water.
 12. The method of claim 11 comprising exposing at least thenon-removal areas to liquid water at least one of during or after thedeveloping, the allowing of the impinging radiation through the secondradiation transmissive regions reducing amount of outer surface watermarks in the non-removal areas of the photoresist post-develop thanwould otherwise occur under identical processing but for said allowingof the impinging radiation through the second radiation transmissiveregions.
 13. A method of lithographically patterning a substratecomprising photoresist which has removal areas and non-removal areas,the photoresist having a develop drop-off point for a selected incidentradiation wavelength, the method comprising: providing a mask over thephotoresist, the mask having first radiation transmissive regions andsecond radiation transmissive regions, the second radiation transmissiveregions being less transmissive of radiation of the selected wavelengththan the first radiation transmissive regions; impinging the radiationof the selected wavelength onto the mask, an incident dose of radiationbeing at least 4.0 millijoules, the impinging radiation increasing aphotoresist post-develop root mean squared surface roughness by at least25%, the mask allowing the impinging radiation through the secondradiation transmissive regions which is below and within 30% of thedevelop drop-off point to be ineffective to change photoresistsolubility in a developer for the photoresist to be cleared from thenon-removal areas upon developing with the developer, the mask allowingthe impinging radiation through the first radiation transmissive regionswhich is at or above the develop drop-off point effective to change thephotoresist solubility in the developer for the photoresist to becleared from the removal areas upon developing with the developer; afterthe impinging, developing the photoresist with the developer effectiveto clear photoresist from the removal areas and to leave photoresist inthe non-removal areas that has outer surface roughness in thenon-removal areas which is greater than that before the impinging; anddirectly after the developing, exposing at least the non-removal areasto water.
 14. The method of claim 13 wherein the allowing of theimpinging radiation through the second radiation transmissive regions iseffective to increase the photoresist outer surface roughness in thenon-removal areas at least after the developing.